Philippe Durand and Marie-Hélène Perrard at the biotechnology company Kallistem in Lyon, France, say that their method coaxes seminiferous tubules – tissue that produces sperm in the testes – taken from humans, rats or monkeys into producing mature sperm cells.

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A team in Japan made mouse sperm in the lab in 2011, but the French researchers claim they are the first to do this in humans. After 20 years developing their method, they say they can turn the progenitor cells that are inside seminiferous tubules, called spermatogonia, into mature sperm. If true, this would be the first method to complete the final steps in making human sperm, although other labs have managed to push cells through some of the earlier stages. “It’s the final 20 per cent of the process,” says Durand

Sperm in 72 days

Their aim is to freeze tissue from pre-pubescent boys who need cancer treatment, so that they would still be able to father children in later life. Spermatogonia can be destroyed through radiation or chemotherapy, and boys who have not yet reached adolescence would be unable to have sperm samples frozen for use in adulthood.

The team hopes to begin clinical trials in 2017, but this depends on getting permission to use lab-made sperm to fertilise a human egg. “We must make sure it’s safe, ethical, secure and acceptable for the patients and regulatory agencies,” says Perrard.

In the meantime, the team plans to refine the technique to increase yields of sperm. The method involves suspending bundles of extracted seminiferous tubules in small cylinders of a water gel called chitosan. These are then immersed in a dish containing a solution of nutrients, vitamins, hormones and growth factors, and the dish placed inside a bioreactor. The team says the process for human sperm takes 72 days, after which the cylinders are removed, the gel dissolved and the sperm extracted.

Stem-cell experts are declining to comment on the team’s patent, saying that they will reserve judgement on the technique until the team has published results in a peer-reviewed journal. Durand and Perrard say they are currently preparing a paper. “It’s very important for us to have it published,” says Perrard.